(Newser)
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The Centers for Disease Control and Prevention has prepared a seed stock of vaccine for the swine flu that has killed dozens in Mexico and infected a handful of Americans, Time reports. The CDC has not begun mass production of the vaccine, opting instead to see if the outbreak reaches pandemic proportions. Still, “concern has grown” about the virus, an official said.

The CDC is working with the World Health Organization to monitor the spread of the virus, and vaccine production could be fast-tracked if the flu case-load grows. The distance between US cases—reported in California and Texas—worries officials, because it indicates the virus is easily transmitted between people. The CDC has not said what level of infection would necessitate rolling out the vaccine.